The present invention relates to rotary positive displacement engines and to methods for determining engagement surface contours for use in the making of rotary positive displacement engines.
This invention concerns an advanced rotary positive displacement engine having high power to mass ratio and low production cost. The term xe2x80x9cenginexe2x80x9d as used in this patent document is taken to be a device that converts one form of energy into another. Hence, the term includes both devices which impart energy to the fluid flow (e.g. a pump) and those which employ the fluid flow to generate an energy output (e.g. an external combustion engine for providing a power source).
In the case of prior art combustion engines, the reciprocating piston type is most widely used for its low cost of production and efficient sealing, while the turbine has shown that an external combustion engine may offer greater power, partially from high speed. Rotary engines such as the Wankel engine have shown higher power-to-weight ratios than reciprocating engines but at the expense of increased fuel consumption. The present invention is a rotary device that offers many of the advantages of these prior art devices without many of their shortcomings.
In the case of pumps, there are many general types of pump designs known, such as positive displacement, centrifugal and impeller. Pumps of the positive displacement type are typically reciprocating or rotary. Many previous rotary combustion engine designs in turn, have been of the single plane type in which rotary motion occurs about axes that are parallel to each other.
Prior forms of rotary pumps and combustion engines have been limited in their efficiency, in part by inherent limitations in their operating principles, and also in many instances by their inability to establish a seal between operating surfaces which is sufficient to achieve a high degree of efficiency, yet which also accommodates the physical characteristics of the fluid which much pass therethrough.
Many of the deficiencies of prior types of rotary pumps and engines have been negated by a positive displacement engine which has been developed by Applicant (referred to from time to time herein as a xe2x80x9cCvR Enginexe2x80x9d) and, which is disclosed in issued U.S. Pat. No. 5,755,196, the entirety of which is hereby incorporated by reference herein. The present invention, however, provides several significant improvements and advances which are applicable to the CvR engine design which is disclosed in U.S. Pat. No. 5,755,196.
For example, as the demand for higher performance and higher efficiency are increased, machining techniques have also been improving.
At the same time, however, different applications may require various clearances and interferences between the surfaces not always the closest possible fit. For example, the movement of fluids with suspended particles may require large enough sealing surface clearances to allow these solids to pass through in the fluid film. In some applications, such as irrigation pumping, these particles may be in excess of 0.1xe2x80x3. In other applications, such as in the semi-conductor or medical industries, the particle size can be as small as several microns. Hence, there are many applications where it is essential to establish a finite, precisely controlled gap between the two sealing surfaces to provide a positive sealing surface geometry (SSG).
Similarly, where comparativily low tolerance manufacturing techniques are used to produce lower performance or less expensive designs, a sealing surface geometry (SSG) which allows for the inconsistencies of the final surface. Higher tolerance machining techniques will also benefit from a predetermined SSG to maintain a minimum gap clearance or to prevent contact or binding of the mating rotors. Hard coating of a suitable base material also requires a pre coated surface geometry which prevents the coated SSG from binding or interfering.
Some applications may even benefit from an interfering or xe2x80x9cnegativexe2x80x9d SSG. Compressible or deformable materials and coatings can provide increased seal performance if they are designed to interfere with the mating surface on the opposite rotor. This can be accomplished by applying such a coating over a harder base material having a negative SSG to bring the surface back to a reduced negative SSG, so as or a positive SSG.
Another advantage made possible by an extremely precise SSG is the espablishment of a fluid fild bearing between the sealing surfaces. Fluid film bearings have been used successfully in industry to replace ball bearings or plain bearings in many applications. Fluid films for bearings range from several ten thousandths of an inch to several thousandths of an inch. Having a fluid film between the sealing surfaces of the engine rotors will decrease friction and wear, however, establishing this fluid film requires a correctly designed surface interface. If the surface interface has a gap space which does not account for the other variables which affect the fluid film; however, extra friction and wear, as well as volumetric efficiency compromises, may result.
An excessive clearance or gap between the sealing surface, may lead to excessive leak-by, thereby significantly impairing the overall efficiency of the engine. For example, if excessive xe2x80x9cbacklashxe2x80x9d develops between the sealing surfaces of the CvR(trademark)-type engine described above, this can result in undesirable amounts of leak-by.
An additional concern is that for many applications it is desirable for the engine to be highly efficient in both forward and reverse directions of operation. Consequently, if the sealing surfaces of the engine are able to move apart and create an excessive back-lash, due to deficiencies in the desired SSG or for other reasons the engine will be unsatisfactory for reverse operation.
Accordingly, there exists a need for a method for determining the contours of the sealing surfaces of a rotary engine (as defined herein) so that these will have a precise, controlled gap during operation of the pump. Furthermore, for manufacturing purposes, there exists a need for a method for verifying that the correct contours have been imparted to such surfaces. Still further, there exists a need for an engine having such surfaces arranged so that the proper gap will be maintained during both forward and reverse operation.
The present invention is of the rotary positive displacement type, but is in a class by itself. This rotary positive displacement device is believed to be the first rotary engine in which the axes of the moving parts are offset from each other and the moving parts rotate at a constant velocity relative to each other when they are rotating at a constant velocity relative to the casing. The engine is formed by a pair of facing rotors that are axially offset from one another and whose faces define chambers that change volume with rotation of the rotors.
An engine of this type defines a new class of engines, and includes a minimum number of moving parts, namely as few as two in total.
In one aspect of the invention, a pump includes a pair of rotors, both housed on and preferably within the same housing. The housing has an interior cavity having a center. Each rotor is mounted on an axis that passes through the center of the cavity, the respective axes of the rotors being at an angle to each other, with the center of each rotor being at the center of the cavity. The rotors interlock with each other to define chambers. Vanes defined by a contact face on one side of the vane and a side face on the other side of the vane protrude from the rotors. The contact faces of the rotors are defined so that there is constant linear contact between opposing vanes on the two rotors as they rotate. The side faces are preferably concave and extend from an inner end of one contact fact to the outer end of an adjacent contact face, equivalent to the tip of a vane. The side faces and contact faces define walls of chambers that change volume as the rotors rotate. Ports for intake and exhaust are preferably configured to have shapes complementary to the intersecting vanes of the rotors.
Also in accordance with the present invention, a method is provided for determining a precise, controllable gap between the sealing surfaces on the rotors. These methods include both mathematical and geometric processes, a well as methods for verifying that the correct contours have been imparted to the surfaces.
Still further, in accordance with a preferred embodiment of the invention, the vanes on the rotors are provided with mirror-image contoured sealing surfaces which both maintain the desired gap during operation by reducing back-lash, and which also permit efficient reverse operation of the engine.
These and other aspects of the invention will be described in more detail in what follows and claimed in the claims appearing at the end of this document.